<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>JS引入模式</title>
</head>
<body>
    <button id="bt">来啊快活啊</button>
</body>

<!--<script>
    document.getElementById("bt").onclick=function () {
        alert("hahaha")
    }
</script>-->
<script src="js/demo01.js"></script>

</html>